Electrical capacitors are used in a variety of applications. Capacitors are generally referred to as large capacitors and small capacitors. Large capacitors include high voltage (greater than 600 volts AC) and low voltage power capacitors, induction heating capacitors, and power factor correction capacitors. Small capacitors are typically found in application categories, such as motor start and run capacitors and lighting capacitors.
One common configuration for electrical capacitors includes a spiral-wound configuration with a pair of capacitor roll sections. Each of the capacitor roll sections is typically a strip of polypropylene having an aluminum or zinc coating. Suitable electrical leads are attached to the spiral-wound roll using conventionally known techniques. The spiral-wound roll is then placed in a casing and the casing is filled with a capacitor fluid.
The capacitor fluids should have a high dielectric constant, maintain a low dissipation factor, and be compatible with other materials in the capacitor. The capacitor fluids must also withstand elevated and fluctuating temperature, pressure, and voltage stress conditions to provide the capacitor with a long operative life.
The capacitor fluid should also be relatively viscous to minimize loss of the capacitor fluid from the capacitor if the casing of the capacitor develops a leak. Additionally, components used in fabricating the capacitor fluid should be biodegradable to minimize environmental damage if the capacitor fluid leaks from the capacitor.
Cichanowski, U.S. Pat. No. 4,388,669, which is assigned to the assignee of the present application, describes polypropylene glycol dielectric fluids. The polypropylene glycol dielectric fluids exhibit high clearability by virtue of low carbon to hydrogen ratio and high weight percentage of molecular oxygen. The polypropylene glycol dielectric fluids also display low swelling effect on the polypropylene film and minimal penetration into the capacitor roll. One drawback of the polypropylene glycol dielectric fluid is that it can leak from a breached capacitor because the polypropylene glycol dielectric fluids possess only moderate viscosities in the range of 500 centipoise.
Bentley, U.S. Pat. No. 4,656,558, discloses a dielectric liquid containing polybutene with an average molecular weight of at least 800. Bentley, U.S. Pat. No. 4,787,010, describes forming a dielectric material from a mixture of polybutene and polyethylene. Bentley '010 indicates that the dielectric material is semi-solid to prevent the dielectric material from escaping from a capacitor in which the dielectric material is used. Using dielectric materials formed from polybutene present problems in obtaining desirable clearance results because polybutene lacks molecular oxygen.